Full Wave Rectifier Circuit

- notes and details of the diode full wave rectifier circuit often used in power supplies and other applications..

The full wave rectifier circuit is one that is widely used for power supplies and many other areas where a full wave rectification is required.

The full wave rectifier circuit is used in most rectifier applications because of the advantages it offers. While it is a little more complicated, this normally outweighs the disadvantages. However sometimes it may not be optimum or necessary to use a full wave rectifier circuit.

Full wave rectifier operation

The concept of the full wave rectifier is that it utilises both halves of the waveform to provide an output and this greatly improves its efficiency.

Comparison of full and half wave rectifier circuits
Comparison of full and half wave rectifier circuits

A further advantage when used in a power supply is that the resulting output is much easier to smooth. When using a smoothing capacitor, the time between the peaks is much greater for a half wave rectifier than for a full wave rectifier.

The smoothed waveforms from full wave and half wave recifiers showing how full wave rectification enables better smoothing and lower ripple levels to be achieved.><br>
<b> Smoothed waveform from diode rectifier circuit </b></center></p>

<p>It can be seen from the circuit diagram, that the fundamental frequency within the rectified waveform is twice that of the source waveform - there are twice as many peaks in the rectified waveform. This can often be heard when there is a small amount of background hum on an audio circuit.</p>

<h2>Full wave rectifier advantages and disadvantages</h2>
<p>Although the full wave rectifier circuit requires more diodes than a half wave rectifier circuit, it has advantages in terms of utilising both halves of the alternative waveform to provide the output.</p>

<TABLE class= Advantages Disadvantages
  • Utilises both halves of the AC waveform
  • Easier to provide smoothing as a result of ripple frequency
  • More complicated than half wave rectifier
  • The twice frequency hum on an audio circuit may be more audible

Types of full wave rectifier circuit

There are two main forms of full wave rectifier circuit that can be used. Each type has its own features and is suited for different applications.

  • Two diode full wave rectifier circuit:   The two diode full wave rectifier circuit is not so widely used with semiconductor diodes as it requires the use of a centre tapped transformer. However this rectifier circuit was widely used in the days of thermionic valves / vacuum tubes. As a rectifier circuit using four valves would be large, the two diode version was much more preferable. The basic circuit is outlined below:

    The circuit diagram of a full wave diode rectifier showing the rectifier and centre tapped transformer
  • Bridge rectifier circuit:   The full wave bridge rectifier circuit configuration is far more widely used these days. It offers a more efficient use of the transformer as well as not requiring a centre tapped transformer. The additional cost is two additional diodes - not an expensive addition these days. Often four diode bridges can be bought as single items, making construction of the overall circuit much simpler. The basic circuit is outlined below:

    The circuit diagram of a full wave diode rectifier showing the bridge rectifier and operation

More complete details of both of these formats of rectifier circuit are given in the following pages. They detail more in-depth information about the circuit, its operation, and requirements for the diodes.

In view of their advantages, full wave rectifier circuits are virtually always used in preference to half wave circuits. The increased efficiency coupled with the better smoothing ability arising from the shorter time between peaks means that their advantages outweigh the disadvantages by a long way. Only occasionally, often for low requirement supplies would a half wave rectifier be used in preference to the full wave rectifier circuit.

By Ian Poole

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